protected override void OnRenderFrame(FrameEventArgs e)
{
// set up viewport
GL.Viewport(0, 0, Size.X, Size.Y);
// clear the back buffer
GL.Clear(ClearBufferMask.ColorBufferBit | ClearBufferMask.DepthBufferBit);
// set up modelview and perspective matrix
SetupPerspective();
// set uniforms
_program.CenterMass.Set(_centerMass);
_program.TimeStep.Set((float)e.Time);
_program.ModelViewProjectionMatrix.Set(ModelView * Projection);
// set up binding of the shader variable to the buffer object
_vao.BindAttribute(_program.InPosition, _buffers.Ping);
_vao.BindAttribute(_program.InVelocity, _buffers.Ping, 16);
// set target buffer for transform feedback
// the two outputs are interleaved into the same buffer
// so we only have to bind one of them as both binding indices are equal:
// _program.OutPosition.Index == _program.OutVelocity.Index
// when you choose to write into different buffers you need to bind all of them
_feedback.BindOutput(_program.OutPosition, _buffers.Pong);
// render the buffer and capture transform feedback outputs
_feedback.Begin(TransformFeedbackPrimitiveType.Points);
_vao.DrawArrays(PrimitiveType.Points, 0, _buffers.Ping.ElementCount);
_feedback.End();
// swap all the buffers!
_buffers.Swap();
SwapBuffers();
}
